Mixed salts for lithium iron phosphate-based batteries operated at wide temperature range

To achieve good performance for LiFePO4-based batteries operated at a wide temperature range, mixed salts of LiBF4-LiBOB (lithium bis(oxalato)borate) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide)-LiBOB were investigated as alternative lithium salts to LiPF6 in non-aqueous electrolytes. LiFePO4/Li half cells using LiPF6, LiBF4-LiBOB and LiTFSI-LiBOB slats as lithium salts were investigated by galvanostatic cycling, cyclic voltammetry, thermogravimetric analysis. The results show that LiBF4-LiBOB and LiTFSI-LiBOB mixed salts are much more thermally stable than LiPF6. Corrosion of Al foil in the LiTFSI-based electrolytes can be suppressed successfully by the addition of LiBOB as a co-salt. The electrochemical performance of LiBF4-LiBOB and LiTFSI-LiBOB mixed salts based cells are both better than that of LiPF6-based cell. LiTFSI-LiBOB mixed salt based electrolyte is considered to be a very promising electrolyte candidate for Li-ion batteries that will be used in wide-temperature applications.